Blanking plugs are utilized in the oilfield to plug and seal the flow bores of oilfield tubular members such as tree caps and tubing hangers. Oftentimes it is necessary to close the flow bore of an oilfield tubular member for flow control purposes. Typically, the oil field tubular member includes a plurality of latch grooves in its inner cylindrical wall and an inner annular landing shoulder disposed a predetermined distance below the latching grooves. The landing shoulder is typically formed by a reduced diameter portion which also serves as a seal bore for establishing a metal-to-metal seal with a sealing assembly mounted on the blanking plug.
One type of prior art blanking plug includes a locking mandrel having a tubular body with a lower threaded end for threadingly engaging a blind plug to close the bore of the locking mandrel. Above the blind plug is mounted a packing assembly which typically includes chevron seals disposed between a downwardly facing annular support shoulder on the tubular body and a lower backup ring. The chevron seals are high interference seals which sealingly engage the seal bore of the oilfield tubular member below the landing shoulder. The locking mandrel further includes a plurality of keys spring biased outwardly through windows in the wall of the tubular body. An expander sleeve is initially maintained in an upper position by shear pins which are subsequently sheared to allow the expander sleeve to move downwardly to shift and maintain the keys in their radial outward position for latching in the latching grooves of the oilfield tubular member. A fish neck is mounted on the upper end of the tubular body for lowering the blanking plug on a running tool into the bore of the oilfield tubular member.
In operation, the prior art blanking plug is run into the bore of the oilfield tubular member on the running tool and the packing assembly initiates its entry into the seal bore. Because of the high interferences of the seals, packing assembly resists entry into the seal bore. However, the high interference seals must be sufficiently inserted into the seal bore so that the support shoulder lands on the landing shoulder and thus the keys are in alignment with the latching grooves in the oilfield tubular member. To force the high interference seals into the seal bore, spang jars, located above the running tool, jar down on the blanking plug to drive the high interference seals into the seal bore. Oftentimes, it is necessary to literally beat these seals into place.
It is often difficult to determine whether the high interference seals are sufficiently disposed within the seal bore such that the blanking plug has landed on the landing shoulder. The only indication of proper landing is the metal-to-metal contact as the spang jars are pulled up and let go to jar down on the blanking plug. If the blanking plug does not land on the landing shoulder, the keys cannot expand radially outward into the latching grooves.
Using the jars to hammer the high interference seals into place, can prematurely shear a pin which holds the expander sleeve. If the pin is sheared, the keys are free to shift radially outward through the windows in the tubular body. Thus, the keys become actuated prior to aligning with the latch grooves in the oilfield tubular member even though the blanking plug has not reached the landing shoulder and is not latched into place within the oilfield tubular member. Since the high interference seals have been partially inserted into the seal bore, a pressure test on top of the blanking plug will show that the blanking plug is holding pressure and suggests that the blanking plug is locked into place when in fact it is not because the blanking plug has landed high and the keys are not aligned with the latching grooves. If the blanking plug is not locked in place, upon exposure to downhole pressure, the pressure below the blanking plug will cause the blanking plug to shoot upwardly within the bore of the oilfield tubular member.
The prior art requires jarring down to set the seals, then jarring down to set the locking keys, and then jarring down to release the running tool. There is never a positive indication that these operations have been properly completed. It is possible to jar down and obtain a partial setting of the packing assembly and then release the running tool without having the locking keys in place in the latching grooves. The pressure test from the top suggests that everything is in place. However, as soon as pressure acts on the bottom of the blanking plug assembly, the blanking plug assembly blows up the hole.
The method and apparatus of the present invention overcomes the deficiencies in the prior art.